Dead Pixel Test

The dead pixel test fills your screen with a solid color. Press "Start test" and nine colors will run one after another: first red, green and blue, then white and black, then gray, cyan, magenta and yellow. The tiles above the button jump straight to any color you pick. A small caption in the corner shows the color name, its number, and what you can spot on it. A click or the right arrow moves to the next color, the left arrow goes back, and Esc returns you to the page. The buttons labeled "Color cycling" change the colors automatically every 2, 3, 5 or 10 seconds, and the screen stays awake for the whole test. To see how many pixels your screen actually has, open What is my screen resolution.

How to tell a dead pixel from a stuck one

A dead pixel gets no power and shows as a black dot, the same on all nine colors. A stuck subpixel is locked in the on state and glows as a colored dot, visible even on the black fill.

You can tell the two apart in a single pass. Turn on the black fill: a colored dot on black is a stuck subpixel, a black dot on white is a dead pixel. Flashing cannot revive a dead pixel; it is replaced along with the whole panel. And a spot that shows up only on white is more often dirt on the outside or a pressure mark, not a pixel at all.

Should you try flashing

The "Try flashing" button appears after you answer that you saw a colored dot on black. Flashing cycles five colors with five changes per second to shake the stuck subpixel loose. The duration is your choice: 5, 10 or 20 minutes.

It is worth a try, because no other method can bring a subpixel back, and it sometimes works. Start with 10 minutes. Before it starts, the tool warns about seizures caused by flashing light: if a child is nearby, keep the screen out of their sight. You can stop it with a click or Esc. There is no guarantee of success, and the dot may stay exactly as it was.

Bleeding and banding on gradients

The "Bleeding and gradients" button opens two frames: a "Gray gradient" from black to white and a "Color gradient" running through red, green and blue. The transition should stay smooth; bands and steps on it point to a panel fault.

Bright patches along the edges of a black screen are backlight bleeding. On LCD screens even healthy panels have some, so the question is how visible it is. Check in a dark room: on black, bleeding is easiest to see. Uneven backlighting also shows up well on the gray fill.